The field of the invention is systems and methods for an implantable electrode. More particularly, the invention relates to an electrode comprising a grid or array suitable for use in implanted applications including, for example, intracranial applications.
In patients requiring brain surgery, intracranial electrocortical recording and stimulation can provide unique knowledge about a patient's functional brain anatomy. Electrocortical stimulation (ECS) allows for the investigation of brain function by causing a temporary disruption or activation of function. After the electrodes are placed in or on the brain, recording and stimulating can take place intra-operatively or extraoperatively. This electrophysiologic mapping helps doctors to infer the role of those brain areas in neurologic function. This approach is commonly used, for example, in the treatment of medically refractory epilepsy, functional disorders and brain tumors. However, it can be difficult to integrate the results of subdural recordings made during ECS with other brain mapping modalities, particularly functional magnetic resonance imaging (fMRI).
The ability to integrate imaging and electrophysiological information with simultaneous intracranial or subdural electrocortical recording/stimulation and fMRI may offer insight for cognitive and systems neuroscience as well as for clinical neurology, particularly for patients with epilepsy or functional disorders. Unfortunately, standard intracranial electrodes cause significant artifacts in MRI images, and concern about risks such as cortical heating have generally precluded obtaining MRI in patients with implanted electrodes. In the case of cortical heating, the leads or other conductive structures of some electrodes operate as antennas, focusing radio frequency (RF) electromagnetic waves and causing localized heating, which may result in injury. In addition to heating concerns, the structure of existing electrodes can cause a large increase (e.g., 100-fold) in the strength of the magnetic field near the electrode's conductive components creating inhomogeneities of the B0 field as well as artifacts due to the electrode's density. For imaging, this electromagnetic interference can cause disturbances to an MRI scanner's B1 field, an electromagnetic field used for imaging. The metal in the electrodes could also generate artifacts in other imaging systems, such as streaks that degrade the image quality of computed tomography (CT)—this is particularly problematic as the artifacts are generated at the location being examined—the location of interest from which data is being collected. These concerns have prevented the concurrent use of ECS and related technologies in MRI-guided surgeries, reducing the overall effectiveness of ECS.
Conventional intracranial electrodes also present a number of potential post-operative complications including epidural hematoma, subdural hematoma, significant brain edema, brain swelling, infection, and neurological disorders (e.g., transient aphasia, deficits, or status epilepticus). Short term implantation of intracranial electrodes is often used in the evaluation of patients for epilepsy surgery, but this approach is often limited due to these risks.
Increasingly, the option of chronic implantation of electrodes into the central or peripheral nervous system to record or stimulate, or do both in an open or a closed loop system offers therapeutic options for many neurologic diseases. However, the inability to obtain standard MRI in such patients after placement of the devices introduces a consequent risk, moreover, the bulkiness of the hardware with its associated complications makes chronic implantation problematic.